Sudden Aileron Deflection - uncommanded

Would welcome some thoughts. I am an experienced RC pilot but had something happen today that put one of my favorite e-sailplanes in the dirt.

Some background: I am a stickler for proper pre-flights including range checks. My equipment is all quality stuff. My last incident was a carthweel when a sudden crosswind lifted one of my tips on a sailplane last year. I fly three to five days a week (Don't ask how many hours I put in :-))

Ok, the story -- Did my pre-flights on my sailplane today along with a range check. All linkages solid and moving freely. (Note: I am an obsessive "wiggler" and go through that ritual several times as I prepare for launch.) All was normal until my plane left my hand and was only about 30-40 feet away and under full power when the right wing suddenly lifted. It was so sudden, I barely had time to pull back on the throttle and attempt to right the plane. Went in hard snapping my CF boom and ripping off the tail. Some cosmetic damage to the wings but saved my glass pod.

You all know that queasy feeling as you approach your downed plane. Well, wasn't as bad as I thought but I immediately noticed the right aileron fully deflected in the down position while the left aileron was in "neutral". (Note: The plane took the most force on the tail and left wing. The right wing did not come in contact with anything that I could see.) Once I powered down then powered back up, the right aileron returned to its normal position. I then recalled an incident a few weeks ago with the same plane at about 300 feet or so and I experienced a sudden left roll but recovered after some stick movements. I wrote that off to turbulence but now it looks like I may have already experienced this malfunction but didn't realize it as a problem. I tried over and over to recreate that aileron movement but no luck.

Any ideas on what would cause a servo to suddenly deflect like I described? I have my own thoughts but want to see if you guys have some other ideas.

Dave.... I've experienced two instances of what I believe to be "single event upsets" where microprocessor operation glitches because of a cosmic particle collision or for whatever reason. The events were different and an explanation of each would be lengthy, but in both cases, servos were driven hard over.

Technology is a wonderful thing but with it comes functional risk and I think we are seeing a few as time goes by. If one reads a little about single event upsets, it becomes evident that critical software and equipment run parallel programs and processing that auto switch out a glitch to the back up and then auto perform a diagnostic and correction.

Thanks for your input. I was suspecting a kind of "ghost in the machine" scenario as well. I accept your "single event upset" discussion. Once I get the replacement parts on and the repairs made, I plan on clearing the program for that aircraft and re-programming. It is likely that I will replace my aileron servos since they are about eight years old. Already removed my ruddervator servos given that they took a lot of load when the tail boom broke. I tested them and examined closely but found no indication of any stripping but they are also pretty old. Time for some replacements although I suspect that this is indeed a "cosmic glitch" and independent of hardware issues.

The plane I damaged is one of my 2m birds, a Sky 2.0 EV, and a real favorite since it was a gift from my wife and daughters. An excellent flier too. I've attached a photo with the 2m Sky (yellow markings). By the way, that other plane in the pic is also 2m but weighs in at about 18.5 oz!

Thanks again for your thoughtful comments.

Regards,
Dave

Images

I was discussing this issue on another thread... Someone had questioned if his shoot down was because of some nearby towers. Any in your area? We have an antenna farm on a hump about two miles away. I have had one upset, I know of several others over the last few years, including a an Apprentice crash in the last two weeks.

I distinctly remember flying towards the farm and the airplane was in-line between the farm and me. It slipped, dove down and right but picked up in less than a couple of seconds. I had enough altitude to command hard up elevator and get altitude.

I think most flyers here are aware of the problem, and usually don't fly towards the farm (unless we forget... I have). Fortunately it is a pass through area as you cross it more than go inline with it. It happens to be between a wind sock and the edge of a tree line so we tell everybody not to fly towards the farm and don't go between the landmarks.

Nope, no antennas here. I fly way out in farm country. Just me, the deer, bears and wolves (and one dead pheasant today!). Also, my incident involved a single servo so I'm pretty sure no generalized interference. As I described, that servo went hard to its limit of travel and you can read the rest. Frustrating but rare and an unwelcome part of our hobby. I have been present when other fliers experienced temporary loss of control from what was most probably interference but that goes back to my 72Mhz days.

Was the servo trashed? If not, give it a good check with a tester. I read up on another issue where if the throws aren't correct some pitting occurs and can cause failure. Not sure if this would cause full deflection though.

Servo seems fine. Returned to neutral position after I shut down and powered back up. Ran it though its paces on my tester. No issues so I'm going to chalk this up as a one-off cosmic event but will retire my servos. I have new servos on the way since I have repairs to make anyway and the servos I have have been flying in that plane for eight years. And I fly --- lots!! I can't ask for better service from these things. They're Hitec HS 65-HBs. Replacing with digital. I'm just grateful that my plane will be back in the air soon, not that I don't have plenty of others to fly. A point my wife comments on!

I'll attempt to describe the two instances I think were single event upsets.

The first.... my aerobatic plane suddenly rolled. I fought the roll but lacking pitch control it went down but I was able to get the wings level before it hit which saved the wings but the whole front section of my giant scale was damaged. When rebuilding I discovered that the elevators were hard over in opposite directions, hence the cause of the roll and loss of elevator control. The cause was preserved in memory. It took unticking the slave ch from the master elevator to clear the problem. Immediately reassigning the same slave setup and all was working correct again. I'd flown that setup for months prior to the crash and since the rebuild, now for about two years without a further problem.

The second did not cause a crash. With no input, the plane suddenly did a snap roll, with all surfaces going hard over but it only lasted about two seconds. I immediately landed thinking a momentary signal loss had occurred but didn't understand why the fail safes had not come into effect. Before shutting off the receiver, I shut the transmitter off to verify that fail safes were working properly.... and to my great surprise, everything went hard over as if snap rolling. It verified that indeed I had lost signal momentarily and fail safe had caused the snap roll.

The question was, why did it do that as I was certain that the fail safe had been setup to go neutral controls except on throttle and it was to go to idle. The throttle was now going wide open and the rudder, ailerons and elevator hard over. Turned the TX back on, everything went normal, turned it back off and all went hard over. At that point, I shut the RX switch off. Moments later some guys came over and asked what was up? I explained that when losing signal the fail safe had taken everything hard over yielding an unwelcomed snap roll. Here, I'll show you and all was turned on and then the TX turned off to kill the signal... again, to my great surprise... fail safes worked nominally. The fail safe glitch was not preserved in memory (as the elevator glitch had been) and was cleared when powering the receiver down .

Servo seems fine. Returned to neutral position after I shut down and powered back up. Ran it though its paces on my tester. No issues so I'm going to chalk this up as a one-off cosmic event but will retire my servos. I have new servos on the way since I have repairs to make anyway and the servos I have have been flying in that plane for eight years. And I fly --- lots!! I can't ask for better service from these things. They're Hitec HS 65-HBs. Replacing with digital. I'm just grateful that my plane will be back in the air soon, not that I don't have plenty of others to fly. A point my wife comments on!

Dave

So are you saying the RX was still powered up when you got there?

I'm thinking the force of the crash caused that aileron to swing under its own weight and manually force that servo to the extreme limit. But it should have gone back to neutral if the Rx remained powered up and everything connected.

You say the servo returned to neutral after you shut down and powered back up. Shut down what? The Tx? Rx? or both? And what brand, model etc of Tx and RX is it?

Any connections that were disconnected? Even slightly? And what were they?

Can you walk us through the steps you took as you approached the crash and surveyed the scene?

The question I think needs to be answered is, did the servo put the aileron there (full deflection) or did the aileron put the servo there? Make sense?

I fly Hitec equipment. TX is fine. Fly many other planes on it. No issues.

My plane is a sailplane. If you look at my OP, you'll see that the aileron was not affected by any other contact. Since it's a very light plane, ailerons do not deflect or droop as a result of gravity.

I'm comfortable with the conclusions I have arrived at along with AA's comments. I appreciate all your input but will be bowing out now.

If any surfaces go to full defection it cant be a signal loss issue as the failsafe will set the surfaces to neutral (again assumes its correctly set up and that is what was programmed).

A uncommanded deflection is nearly always an issue at the TX end. Most new TX's use digital pots on the sticks however older transmitters still use wiper pots (ie same as a volume control on a stereo). The issue here is that they do wear. TX's did used to get serviced. This involved blowing out all the pots with compressed air and giving them a dose of electrical contact cleaner.

I am not sure what era you Hitec is but for instance first gen DX6i's were well known for this and I think Horizon even issued a service notice on them at one stage.

If any surfaces go to full defection it cant be a signal loss issue as the failsafe will set the surfaces to neutral (again assumes its correctly set up and that is what was programmed).

A uncommanded deflection is nearly always an issue at the TX end. Most new TX's use digital pots on the sticks however older transmitters still use wiper pots (ie same as a volume control on a stereo). The issue here is that they do wear. TX's did used to get serviced. This involved blowing out all the pots with compressed air and giving them a dose of electrical contact cleaner.

I am not sure what era you Hitec is but for instance first gen DX6i's were well known for this and I think Horizon even issued a service notice on them at one stage.

Cheers

Shaun B

Shaun... saying that something can't happen seems a bit cavalier. My experience contradicts the assertion. It might be a fair statement that it won't happen if fail save programming is working nominally, but when micro processors are involved, we know that the abnormal can happen, even if rarely.

I'm not saying that it was failsafe operation that drove the OP's aileron servo hard over, I'm saying it was what drove all my servos hard over. Thus saying it can't happen... is disproved by the fact that it has happened.

Shaun... saying that something can't happen seems a bit cavalier. My experience contradicts the assertion. It might be a fair statement that it won't happen if fail save programming is working nominally, but when micro processors are involved, we know that the abnormal can happen, even if rarely.

I'm not saying that it was failsafe operation that drove the OP's aileron servo hard over, I'm saying it was what drove all my servos hard over. Thus saying it can't happen... is disproved by the fact that it has happened.

I agree that a servo can glitch. I have just changed over (warranty) a Hitec HD35 digital I had in a DLG that would not respond to normal inputs and would swing to full travel on one direction then lock. But it did that every time it was powered up.

If both servos are going to full travel regardless of direction (in your case in the same direction assuming the servos are located opposing each other as most aileron servos are) they are getting a signal from the RX and the RX cant generate a signal without an input (ie signal from the TX).

These sorts of issues drive us all nuts. I would always rather put an aeroplane into the ground doing something stupid (don't ask me about my patented figure 9 manoeuvre ) than have something fall out of the sky and be left wondering "what the??".

I agree that a servo can glitch. I have just changed over (warranty) a Hitec HD35 digital I had in a DLG that would not respond to normal inputs and would swing to full travel on one direction then lock. But it did that every time it was powered up.

If both servos are going to full travel regardless of direction (in your case in the same direction assuming the servos are located opposing each other as most aileron servos are) they are getting a signal from the RX and the RX cant generate a signal without an input (ie signal from the TX).

These sorts of issues drive us all nuts. I would always rather put an aeroplane into the ground doing something stupid (don't ask me about my patented figure 9 manoeuvre ) than have something fall out of the sky and be left wondering "what the??".

Regards

Shaun B

"Left wondering" certainly is uncomfortable and I'd encourage a pilot to give best effort to determine and understand the cause.

Exploring the bolded statement above, would I be correct in thinking that the TX sends instruction to the RX regarding what to do upon signal failure (fail safe) and the RX stores and initiates those if communication with the TX fails? If that is true... the RX does have the capability of generating servo signals without TX input.

In my second glitch narration, fail safe was instructing all servos to go hard over. That was verified when back on the ground by turning off the TX and done twice to be certain. Nominal operation of fail safe instructions only resumed after the RX was powered down effecting a receiver reset.

Left wondering is whether the TX sent a bad set of instructions or whether the RX falsely interpreted the instructions and acted on the false interpretation. Which had the communication failure?